1. Field of Invention
The present invention relates to an optical device. More particularly, the present invention relates to a highly reliable optical add/drop device.
2. Description of Related Art
In optical fiber technology, optical add/drop (OAD) devices, sometimes referred as wavelength division multiplexed units, are used to combine or separate optical signals having different wavelengths. The OAD devices have been utilized to significantly enhance the signal capacity of optical communication systems. An OAD system simultaneously transmits multiple information signals on a single waveguide medium at different wavelengths or channels. Examples of such communication systems include telecommunication systems, cable television systems, local area networks (LANs) and wide area networks (WANs). As highly developing of optical communication, the requirements for OAD devices with high performance and reliability are increased.
The reliability of OAD devices generally depends on the designing and packaging technology. In conventional OAD devices, one way to assemble the OAD devices is bonding all optical parts together by applying epoxy. A typical structure of the OAD device includes a dual fiber collimator with a first gradient index (GRIN) lens, a wavelength division multiplexed (WDM) filter and a single fiber collimator with a second GRIN lens. A light beam carried on a plurality of wavelengths are multiplexed together or demultiplexed separately for transmission by the OAD devices. A light beam having different wavelengths is input into a conventional OAD device via one fiber of the dual fiber collimator. The light beam is transmitted to the first GRIN lens for collimating, and then incident on the WDM filter. The light passing through the WDM filter is transmitted to the single fiber collimator. The remainder of the composite signal is reflected back to the first GRIN lens and then transmitted to another optical fiber.
In one type of conventional OAD device, the WDM filter is fixed on one end surface of the first GRIN lens based on epoxy bonding. Therefore, the angle between the filter and the incident light is adjusted to achieve a lowest transmission loss, and fixed. Thereafter, the single fiber collimator and the dual fiber collimator are then packaged by applying a heat-curing epoxy to assemble the OAD device. The conventional packaging structure provides the OAD devices with good performance. However, the OAD devices according to conventional method have a risk of failure when they are operated during temperature variation. In general, the epoxy applied on the edge of the filter and the first GRIN lens non-uniformly expands or shrinks during temperature variation, and tilts the filter. Further, the light beam emitted from the WDM filter may deviate, and thus the insertion loss and reflection loss are increased. Because of the expansion and shrinkage problem of the epoxy, there is still a need in the art to provide new packaging structure by decreasing the usage of epoxy to obtain highly reliable operation.
It is therefore an object of the present invention to provide a reliable OAD device in which a ring is used to mount a filter therein, and thereby prevent the filter from tilting.
It is another object of the present invention to provide a reliable OAD device, in which by soldering the ring with an external tube via the openings at the middle sidewall of the external tube, the ring with the filter therein and other optical parts of the OAD device can be packaged rigidly. Hence, the OAD device can be reliably performed during temperature variation.
In one aspect, the present invention provides a structure for packaging an optical add/drop (OAD) device with a filter. The structure includes a ring and an external tube. At least three corners of the filter contact the inner sidewall of the ring, and the filter tightly wedges in the ring. The external tube has an inner diameter substantially equal to the outer diameter of the ring. The external tube has at least one opening at the middle sidewall, and the ring is positioned in the external tube to block the opening. Moreover, the ring is soldered with the external tube to combine them together.
In another aspect, the present invention provides an optical add/drop device that includes a filter, a ring, an external tube, a single fiber collimator and a dual fiber collimator. At least three corners of the filter contact the inner sidewall of the ring, and the filter wedges in the inner hole of the ring. An external tube has an inner diameter substantially equal to the outer diameter of the ring. The external tube has a middle group of openings in the middle sidewall, and two groups of openings adjacent to the terminal ends of the external tube respectively. As the ring is positioned at the middle of the external tube to block the center openings, the sidewall of the ring is seen via the center openings. The ring is soldered with external tube via the center openings so as to fix the ring in the external tube. The single fiber collimator and the dual fiber collimator are coupled to each other in the external tube by soldering the inner metal tubes with the external tube via the another two groups of openings, respectively.
According to the OAD device of the present invention, the filter can be well fixed in the external tube through the ring. By soldering the ring, the inner metal tube of the dual fiber collimator and the inner metal tube of the single fiber collimator with the external tube via the openings, the optical parts can be well assembled inside the external tube. Therefore, optical path shift in conventional OAD device caused by the degradation and deformation of epoxy can be eliminated to attain high performance and reliability.
The feature of the invention is that the diameter of each center openings is less than the thickness of the ring. As the external tube and the ring are made of metal, the ring and the external tube can be soldered together via the middle openings without utilizing any adhesive material.